Solid electrolytic capacitors are conventionally known in which an anode made of a valve metal is anodized in an aqueous solution of phosphoric acid to form a metal oxide layer serving as a dielectric on the surface of the anode and manganese dioxide is used as an electrolyte layer. However, the small electrical conductivity of manganese dioxide presents a problem of increased equivalent series resistance (ESR).
Meanwhile, solid electrolytic capacitors are also known which are aimed at reducing the ESR by using a conductive polymer instead of manganese dioxide as an electrolyte layer.
Such a solid electrolytic capacitor using a conductive polymer as an electrolyte layer has the advantage of reduced ESR as compared to solid electrolytic capacitors using manganese dioxide as their electrolyte layers, but has the problem of increased leakage current. Particularly, for a solid electrolytic capacitor of such kind using niobium for the anode, its oxide layer serving as a dielectric layer is susceptible to heat and also sensitive to stress. Therefore, in the step of forming an outer package as by resin molding or like steps, an injection pressure of resin for resin molding is applied to the dielectric layer to damage the dielectric layer, thereby causing a problem of increasing the leakage current.
To address this, a technique has been developed for reducing the increase in leakage current by applying, before the formation of an outer package by resin molding, a sheet-shaped buffer formed of rubber, paper, fabric or the like only to a surface of the electronic component element facing the gate for molding to relax the resin injection pressure and thereby reduce the damage to the dielectric layer (see Patent Document 1). Patent Document 1: Published Japanese Patent Application No. H08-148392